Earnest is painted light brown with a green tender, brass fittings, and gold lining.
Earnest has no specific basis, and appears to be a freelance design. However, he does strongly resemble a Great Western Railway Star Class, the 2-2-2 broad gauge steam locomotive. A non-working replica of a GWR Star Class named North Star was constructed for the 1923 Cavalcade, and is now housed at Swindon Steam Railway Museum.
- 1984 - Toby and the Stout Gentleman and Thomas in Trouble (portrait cameo)
- 1990 - Thomas in Trouble (portrait cameo)
- 1991 - Thomas Comes to Breakfast (portrait cameo)
- According to a SiF interview, the portrait of Earnest was illustrated by Robert Gauld-Galliers, and was described to be a "made-up character" in the Victorian era to match the various other human portraits featured throughout the series. The portrait was roughly 80 x 60 mm.
- In 2017, Robert Gauld-Galliers confirmed that at the time of production Earnest wasn't named, and suggested he be named 'Earnest'.
- Earnest is the first engine to have a moustache, the second being the Iron Duke and the Third being Etienne.